F the B-Myb TAD may confer several thermodynamic and functional advantages, including the ability to bind to a diverse range of partner proteins with high specificity but moderate affinities, consistent with the formation of transient regulatory complexes [50], [62]. Previous studies with intrinsically disordered TADs have identified regions with the tendency to form amphipathic helices as important interaction sites [58], [63]. Secondary structure predictions for the B-Myb TAD suggest the potential to form two short helices between residues Tyr290 and Ala297 (YKWVVEAA) and residues Ser307 and Glu316 (SLSEALDLIE). Helical wheel analysis of these regions reveals that the helices formed would be amphipathic (figure 6) and contain extensive hydrophobic faces for interaction with functional partner proteins such as p300. Interestingly, the two potential helices are contained within a 47 residue region of B-Myb (Pro289-Ser335 in mouse) that is highly conserved between human, mouse, chicken and zebrafish (figure S1, 32 sequence identity and 26 sequence similarity).Figure 6. Potential amphipathic helices in the B-Myb TAD. Panels A and B show helical wheel representations of the regions of the B-Myb TAD predicted to form amphipathic helices, charged residues are underlined and polar residues shown in italics. The positions of the helical regions were predicted using the programme PSIPRED [71], [72]. doi:10.1371/journal.pone.0052906.gacceptable 15N/1H HSQC spectra for samples containing equivalent molar amounts of 15N-labelled p300 TAZ2 and unlabelled B-Myb TAD and precludes any possibility of obtaining assignments for either protein in the B-Myb TAD-p300 TAZ2 complex. The effects seen are characteristic of the formation of a protein complex in intermediate exchange on the NMR time scale, which is reflected 18325633 in the fact that HSQC spectra of the complex obtained at 600 MHz were significantly better than spectra acquired at 800 MHz. The minimal chemical shift changes observed for the backbone amide signals of the TAZ2 domain induced by the binding of B-Myb TAD are summarised in the histogram shown in figure 5B, The minimal shifts of signals from a small number of non-proline residues (Ser1726, Cys1801, Val1803, Phe1805, Cys1806, Title Loaded From File Leu1807, Asn1808 and Ile1809) in TAZp300 TAZThe TAZ2 domain of p300/CBP is an important proteinprotein interaction site and has been reported to bind a multitude of functional partners involved in the regulation of Title Loaded From File transcription, including the adenovirus E1A oncoprotein and p53 [61], [64], [65], [66]. The p300 TAZ2 domain was produced as inclusion bodies in E. coli and refolded by dialysis in the presence of an ,5 fold excess of zinc ions. CD and NMR spectra of the isolated p300 TAZ2 domain clearly show that it forms a folded globular domain, which is stabilised by the binding of zinc ions. The far UV CD spectra also indicate that the domain contains a large proportion of regular helical structure.Features of the B-Myb TAD-p300 TAZ2 ComplexFeatures of the B-Myb TAD-p300 TAZ2 ComplexFigure 7. Comparison of the B-Myb, 11967625 STAT1, E1A and p53 transactivation domain binding sites on p300/CBP TAZ2. Panel A shows a contact surface view of CBP TAZ2 (top) with the location of the B-Myb TAD binding site on p300 TAZ2 highlighted as described in figure 5. For comparison, the structures of STAT1 TAD-CBP TAZ2 (row 2; PDB code 2KA6), E1A CR1-CBP TAZ2 (row 3; PDB code 2KJE) and p53 TAD1-p300 TAZ2 (row 4 PDB code 2K8F) are shown in the same o.F the B-Myb TAD may confer several thermodynamic and functional advantages, including the ability to bind to a diverse range of partner proteins with high specificity but moderate affinities, consistent with the formation of transient regulatory complexes [50], [62]. Previous studies with intrinsically disordered TADs have identified regions with the tendency to form amphipathic helices as important interaction sites [58], [63]. Secondary structure predictions for the B-Myb TAD suggest the potential to form two short helices between residues Tyr290 and Ala297 (YKWVVEAA) and residues Ser307 and Glu316 (SLSEALDLIE). Helical wheel analysis of these regions reveals that the helices formed would be amphipathic (figure 6) and contain extensive hydrophobic faces for interaction with functional partner proteins such as p300. Interestingly, the two potential helices are contained within a 47 residue region of B-Myb (Pro289-Ser335 in mouse) that is highly conserved between human, mouse, chicken and zebrafish (figure S1, 32 sequence identity and 26 sequence similarity).Figure 6. Potential amphipathic helices in the B-Myb TAD. Panels A and B show helical wheel representations of the regions of the B-Myb TAD predicted to form amphipathic helices, charged residues are underlined and polar residues shown in italics. The positions of the helical regions were predicted using the programme PSIPRED [71], [72]. doi:10.1371/journal.pone.0052906.gacceptable 15N/1H HSQC spectra for samples containing equivalent molar amounts of 15N-labelled p300 TAZ2 and unlabelled B-Myb TAD and precludes any possibility of obtaining assignments for either protein in the B-Myb TAD-p300 TAZ2 complex. The effects seen are characteristic of the formation of a protein complex in intermediate exchange on the NMR time scale, which is reflected 18325633 in the fact that HSQC spectra of the complex obtained at 600 MHz were significantly better than spectra acquired at 800 MHz. The minimal chemical shift changes observed for the backbone amide signals of the TAZ2 domain induced by the binding of B-Myb TAD are summarised in the histogram shown in figure 5B, The minimal shifts of signals from a small number of non-proline residues (Ser1726, Cys1801, Val1803, Phe1805, Cys1806, Leu1807, Asn1808 and Ile1809) in TAZp300 TAZThe TAZ2 domain of p300/CBP is an important proteinprotein interaction site and has been reported to bind a multitude of functional partners involved in the regulation of transcription, including the adenovirus E1A oncoprotein and p53 [61], [64], [65], [66]. The p300 TAZ2 domain was produced as inclusion bodies in E. coli and refolded by dialysis in the presence of an ,5 fold excess of zinc ions. CD and NMR spectra of the isolated p300 TAZ2 domain clearly show that it forms a folded globular domain, which is stabilised by the binding of zinc ions. The far UV CD spectra also indicate that the domain contains a large proportion of regular helical structure.Features of the B-Myb TAD-p300 TAZ2 ComplexFeatures of the B-Myb TAD-p300 TAZ2 ComplexFigure 7. Comparison of the B-Myb, 11967625 STAT1, E1A and p53 transactivation domain binding sites on p300/CBP TAZ2. Panel A shows a contact surface view of CBP TAZ2 (top) with the location of the B-Myb TAD binding site on p300 TAZ2 highlighted as described in figure 5. For comparison, the structures of STAT1 TAD-CBP TAZ2 (row 2; PDB code 2KA6), E1A CR1-CBP TAZ2 (row 3; PDB code 2KJE) and p53 TAD1-p300 TAZ2 (row 4 PDB code 2K8F) are shown in the same o.
